Nick Clegg, Vince Cable, Chris Huhne (and perhaps even David Cameron and William Hague) might all contest Montgomerie's premise that "One man, more than any other, stands between ­David Cameron and the Tories adopting a sensible, ­popular policy on Europe".

But Montgomerie has drawn up a historic charge sheet of three indictments, where Clarke "has put Europe before loyalty to party and country under at least three leaders" in what amounts to a modern Eurosceptic extension of Churchill's famous indictment of Stanley Baldwin - "Baldwin, Stanley ... confesses putting party before country, 169-70" - in the index of The Gathering Storm.

1. Telling Margaret Thatcher to go in 1990.

2. Preventing John Major pledging referenda on all future Treaties, as well as on the euro, in 1997, so allowing Labour to avoid referenda on Nice, Amsterdam and Lisbon.

3. Appearing with Tony Blair and Peter Mandelson on pro-European platforms, when William Hague was mounting a Eurosceptic campaign to save the pound.

I expect that a public jury would acquit Clarke of the charge of political treason.

And Tory voters see him as an asset rather than a liability to the government, albeit by the relatively narrow margin of 40% to 32% (according to YouGov in January).

Next Left would be unlikely to be given the brief of defending this Tory bruiser. But I think a closer look at the charge sheet can show how Clarke's lawyers ought to be able to find several grounds for mitigation which might lead even a jury of ideologically correct ConservativeHome bloggers to declare the argument of partisan and ideological betrayal not proven.

1. On telling Margaret Thatcher to go, Clarke was the Cabinet minister who was most robust in telling the Prime Minister that her time was up after her pledge to "fight on" in November 1990. He is charged with enjoying the moment too much, and giving the others more courage to say what they had all already decided that they should. But did Clarke's personality make the difference between whether or not Thatcher could survive, having failed to win on the first round of the leadership ballot?

Montgomerie exaggerates Clarke's role and the attribution of these to a pro-EU motive.

Even if we accept the unlikely premise that Clarke was decisive, the charge that this was to put Europe before party surely fails. Here, Clarke's defence team could call John Major as a witness. In his memoir, Thatcher's successor offers some intriguing alternative history. Had he been made Chief Whip (as Thatcher intended), rather than Chief Secretary to the Treasury (at Nigel Lawson's request), Major would not have been much less likely to be catapulted to Foreign Secretary, Chancellor and Prime Minister over the next three years. Yet Major points out that he would have secured Thatcher the four votes she needed to win on the first round (after a famously lacklustre campaign). The Cabinet delegation would have failed, and Thatcher would have been ejected by the voters in the General Election.

On this account, Clarke might be praised for stopping Neil Kinnock becoming PM (with or without LibDem support), and therefore blamed for New Labour.

Except that an alternative account would suggest that Clarke's intervention (if it really had been decisive) stopped Michael Heseltine defeating Thatcher on the second ballot, with new candidates unable to enter the race. In this scenario, by persuading Thatcher to depart, it can be argued that Clarke failed the pro-European cause, in the interests of his party avoiding an even deeper split under Heseltine than the one it was to experience under Major.

2. Blaming Clarke for the lack of a referendum on Amsterdam or Nice is surely a red herring. These are what Trokskyists call 'transitional and provisional demands', since there are no actually existing Eurosceptics who would have been happy with the post-Maastricht EU but opposed to the sovereignty lost at Amsterdam or Nice (or indeed Lisbon). Perhaps a few more do see Maastrict as the moment that the rubicon was crossed (though Montgomerie does not blame Clarke for this), but you will struggle to find many who think that while also being content not to repeal the 1972 Act and British membership. In believing that Britain should stay in the European Union, Clarke is at one with all of his Cabinet colleagues, certainly if we believe their publicly expressed views.

The General Elections of 1997 and 2001 were those (excepting 1983) when the three major parties did offer quite a sharp contrast in attitudes to the EU. Prior to the European Constitution debate, there was little significant Eurosceptic pressure for a referendum with any political or public purchase. In any event, had the Labour government in the 1997-2001 Parliament decided to hold an EU referendum, it would have been much more likely to win than lose, certainly on any subject other than the euro (and possibly even on the euro itself).

3. It was hardly Ken Clarke's fault that William Hague was not a credible candidate for Prime Minister. He could not credibly have been expected to vocally support the "save the pound" aspects of Hague's leadership - and doing so would only have damaged Clarke's own credibility without enhancing Hague's. Here, Montgomerie establishes only sufficient motive for a lesser charge of a willingness to conspire across party boundaries (for or against the national interest, according to ideological taste) in a pro-euro campaign which never in fact took place.

Not even this blog can yet communicate with such distant parallel universes where William Hague was elected Prime Minister in 2001, but it might be suggested that an "in Europe but not run by Europe" government would have been rhetorically Eurosceptic without ever sating the sceptic appetite, perhaps leading to charges of betrayal in the end. (The reason that William Hague is now a pragmatically engaged and nominally Eurosceptic Foreign Secretary is not only a product of Coalition with the LibDems, or a wish to keep Ken Clarke in the Cabinet. It is also a product of being Foreign Secretary for a government and party which believes Britain should remain an EU member).

***

This growing animus against Ken Clarke will not be welcomed in Downing Street.

It could cause Coalition tensions, since the Liberal Democrats would be concerned at the loss of the only Tory who sympathises with them on the EU, though this would be an additional bonus for those making the call for him to quit.

Number 10 is nervous about Clarke's prison reform policy, and have found Clarke stubborn in refusing to split the difference and water it down. (Like Iain Duncan Smith, he has the post-ambition advantage of being happy to walk away if he loses a crucial battle over a policy he cares about). He has, however, begun to pitch his ideas in ways more amenable to the right, recently approvingly quoting Newt Gingrich in a Spectator piece presenting his reforms as robust Tory common sense. (Clarke sees a common sense language - perhaps "bleeding wallet liberalism" - as most likely to build broad public support).

The loss of Ken Clarke from the government appears unlikely, despite the growing chorus of complaint from the right.

Its political impact would go far beyond the criminal justice issue, or a symbolic head on a pike for the Tory Eurosceptics.

The government would lose the one Tory most of the public have heard of - bar Cameron, Osborne and Boris Johnson. That could also be a fatal blow to Cameronism (which is already seen as considerably more right-wing than in May), and would be seen to suggest a narrowing of the Tory party rather than a broader coalition.

This would be welcome to those who think Cameron's "brand decontamination" is nonsense, because it would end it, but very bad for those (like the Prime Minister) who think there was some point to it.

Were Ken booted out in the interests of party purity, it would be difficult to argue that he would then have to keep his mouth shut (in the interests of party unity).

So, against the charge of treachery, Clarke would be able to point only to half a century of active service to the party, including four decades as a Tory MP, as a foundation from which to give his own Tory (albeit pro-European) view of where the national interest lies.

Clarke's dismissal would be unwelcome to the civic and cross-party voices on prison reform who have welcomed his attempts to shift policy.

But those in the Labour party who want to put party first must surely wish more power to the elbow of the Tory right.

Ed Miliband, being a decent sort, might well feel some sympathy with Ken Clarke were he given the boot for offending the Tory right. But, if it did happen, the Labour leader would also have every reason to celebrate.

Ken Clarke's departure from the government would be a disaster for the future of civil rights in this country and for any hope of clawing back some of the rights lost under a succession of deeply illiberal New Labour home secretaries. Clarke's Green Paper on sentencing policy reform, while not by any means ideal, is easily the best thing we can hope for on several fronts, including especially the national scandal of IPPs; and Clarke, with LibDem help, is an essential brake on illiberal proposals, instincts and policies elsewhere in government, especially the home office (as usual).

Clarke's departure would also sound the death knell of Cameron's attempt to rebrand the Tory party as the Nice Party -- not that that would greatly bother me as a Labour junkie. But the removal of his liberalising influence certainly would bother me.